Food packaging

ABSTRACT

The use of a polyolefin film comprising a polypropylene polymer and a polyethylene polymer for the packaging of fresh produce.

This invention relates to a new polyolefin film for packaging food, inparticular to a single or multilayer film comprising polyethylene andpolypropylene components, especially a multilayer film comprisingpolyethylene and polypropylene layers capable of packaging fresh foodssuch as vegetables, fruit, meat and seafood.

The packaging of fresh food products, especially seafood and inparticular fish, is a special challenge for the food packager. Manyfresh foods are moist (or can become wet under pressure) and may alsocontain other natural liquids such as oils and sugary fluids. Freshanimal products will also contain blood and fats and fish will usuallybe wet and hence covered with sea or freshwater, blood, fish oils, iceetc. The presence of all these liquid contaminants makes fresh producemore problematic to package than dry food materials such as pasta orrice. The packaging process and materials for use therein must thereforebe designed to ensure not only that the food retains its quality butalso that none of the substances mentioned above can leak from thepackaging or prevent successful packaging, e.g. prevent sealing beingachieved. It is also essential that the polymer is not degraded ordissolved at all by the liquids present in the product being packaged(i.e. there is no migration from the polymer film to the fresh produce).

Moreover, most fresh produce needs to be carefully handled and packagedto maintain the integrity of the product since products such as fruitand fish tend to damage easily. Much care is therefore needed whenpackaging fresh produce.

It must also be remembered that whilst significant quantities of freshproduce is eaten essentially immediately (i.e within a few days), muchis frozen and hence any packaging material employed in transport andstorage must be suitable for both home and industrial freezing, e.g.down to temperatures as low as −40° C. Moreover, many food consumers nowrequire foods to be packaged in ways which simplify any cooking process,e.g. boil in the bag products or microwaveable products. Ideallytherefore, packaging material for fresh produce should be capable ofbeing boiled or microwaved.

A variety of different packaging alternatives are currently used for thepackaging of fresh produce. For example, fish to be frozen is packagedin plastic or corrugated board containers, e.g. expanded polystyrenecontainers, or on a coated cardboard or plastic support. The support orcontainer is most often supplied with a thin polyolefin film liner andthe entire assembly then frozen rapidly to −40° C.

Much fresh meat is packaged in non-sealed polystyrene containers coveredonly by a polyolefin cling film, i.e. one that adheres to the container.

Lettuce is often packaged in non-sealed plastic wrappers thus limitingits shelf life.

There remains a need therefore to design improved packaging for freshproduce, e.g. fish, in particular to try to eliminate the need forcardboard or plastic containers or supports. Such items are voluminous,expensive to manufacture and are often environmentally unfriendly andpackaging operations using such containers are complicated andrelatively costly.

An alternative to the containers or supports mentioned above is a filmcomprising a polyethylene layer and a polyester (PET), ethylene vinylalcohol (EVOH) or polyamide (PA) layer. Such films can be made bylamination and exhibit good thermal resistance and also act as barrierfilms. Barrier films prevent the diffusion of liquids or gases (such aswater vapour, oxygen or carbon dioxide) from or into the product. Watervapour has low permeability through both polyethylene while gasses suchas oxygen, carbon dioxide and nitrogen penetrate polyethylene readily.PET, EVOH and PA films have low permeability to these gasses but bothpolyamide and EVOH are hygroscopic. It is typical therefore that filmsused for packaging of fresh food products will be packed in a multilayerfilm comprising PE+PA or EVOH in order to minimise ingress of gasses, inparticular oxygen. Meat and vegetables such as potatoes and salads arepacked in these films today.

However, terephthlate, EVOH and polyamide polymers are expensive whichis a serious drawback.

The inventors have surprisingly found a particular polyolefin filmsuitable for the packaging of fresh produce, e.g. fruit, vegetables,dairy products, seafood and meat which is capable of replacing entirelycurrently employed packaging materials. Hence, the film is capable ofreplacing either film lined containers or PA/PET/EVOH films giving riseto a flexible sealed pack which is easy to transport and store.Moreover, the film of the invention is suitable for freezing,microwaving and boiling.

The film of the invention is preferably a multilayer film comprisingpolyethylene and polypropylene layers. U.S. Pat. No. 4,460,631 describesa sealable biaxially stretched film having high scratch resistanceformed from, for example, an isotactic polypropylene and a polyethylenehomo or copolymer with propylene. Such a film is useful for packagingdry foodstuffs such as pasta and rice. Never before, however, have thefilms of the invention been proposed for use in the packaging of freshproduce, in particular produce which contains moisture or othercontaminating liquids, e.g. products such as vegetables, meat orseafood.

Hence, viewed from one aspect the invention provides the use of apolyolefin film, e.g. a multilayer film, comprising a polypropylenepolymer and a polyethylene polymer, for the packaging of fresh produce,e.g. meat or seafood.

Preferably, the invention provides the use of a polyolefin multilayerfilm, e.g. bilayer or trilayer film, having at least a first layer and asealing layer, said first layer comprising a polypropylene polymer,preferably a copolymer with a C₂₋₁₀-alpha olef in and said sealing layercomprising a polyethylene polymer, for the packaging of fresh produce,e.g. meat or seafood.

The term “fresh produce” is intended to cover essentially solid freshfoods that have relatively high levels of liquid content, e.g. watercontent, blood content or oil/fat content and are wet to the touch orwill yield liquid under small amounts of pressure or when cut orpierced. Thus, the term “fresh produce” covers fruit and vegetables aswell as meat, seafood and certain dairy products, e.g. cheese.

Fruit and vegetables may be moist to the touch, e.g. raspberries, oryield moisture when squashed. Cheese may yield oils and fats whenpressurised. Meat and seafood are inherently wet to the touch due toblood, fat and water content.

Preferred vegetables for packaging with the films of the invention arepotatoes, lettuce (including green salads in general), carrots, swedeetc. In a particularly preferred embodiment, the vegetable is one whichis boiled prior to eating and the packaging forms a boil-in-bag product.If necessary, the vegetable may be peeled prior to packaging andprecooked.

The term “meat” used herein refers-to chicken, duck, pork, beef, rabbit,lamb/mutton, venison etc and other edible animals. The term “seafood” asused herein covers all edible marine produce such as fish, shellfish(prawns, crayfish, shrimp etc), crab, lobster, squid, scallops etc.

It is preferred if the films of the invention are used to packageseafood. Most preferably however, the invention concerns the packagingof sea or freshwater fish such as cod, haddock, whiting, salmon, trout,plaice, turbot, bass, tuna, swordfish, mackerel, hake, eel, snapper,skate, herring, catfish, dogfish, marlin, etc. The films may also beused to package fish cakes or other prepared seafood products.

The term “fresh produce” is not intended to cover foods which are dry tothe touch or have, in general low moisture contents, such as pasta, riceand bread. Such foods will not emit liquids under small amounts ofpressure, e.g. those which the product may be exposed to in a shoppingbasket or during a conventional packaging operation.

The fresh produce should preferably be regarded as solid, i.e. the filmsof the invention are not intended for use with liquid produce such ascream. Moreover, the fresh produce should preferably not melt readily,i.e. the films are not intended for the packaging of butter orchocolate.

In its broadest embodiment the film of the invention may comprise asingle layer film formed from a simple blend of polyethylene andpolypropylene polymers. The preferred nature of such polymers isdiscussed in more detail below albeit in connection with multilayerfilms which form the preferred aspect of the invention. Thus, preferredpolyethylene and polypropylene polymers for use in a single layer filmare those preferred for use in each layer of the multilayer film, e.g. apolypropylene copolymer as described below or an LLDPE (linear lowdensity polyethylene) etc.

In the more preferred embodiment of the invention a multilayer film isused to pack the fresh produce which may comprise at least a first layerand a sealing layer.

The sealing layer must be present on an outer surface of the multilayerfilm so that it can be subjected to heat to form a seal around theproduct being packaged. The films of the invention exhibit particularlybeneficial sealing properties since any aqueous contaminants presentwhere the seal is being formed can be evaporated as the sealing processis carried out. When a product such as a fish is transferred onto thefilm prior to sealing it is inevitable that the sealing area will becomecontaminated with water, blood, oils etc from the fish which coulddetrimentally affect the sealing procedure. Since the films of theinvention can be sealed at relatively high temperatures, e.g. greaterthan 130° C., water and the like is evaporated during the sealingprocess giving rise to a much more effective seal. The ability to sealat these temperatures whilst maintaining film integrity in a 100%polyolefin film such as those of the invention is new and forms animportant aspect of the invention. The combination of a polyethylenepolymer and polypropylene polymer in a single or multilayer filmprovides these benefits.

The sealing layer comprises a polyethylene polymer. By polyethylenepolymer is meant a polymer in which at least 70%, preferably at least80%, especially at least 90% by weight of the polymer is made up fromethylene monomer units. In one embodiment, the polyethylene polymer maybe a homopolymer, i.e. where substantially all, e.g. at least 99.5% wtof the monomer units are derived from ethylene e.g. a low densitypolyethylene (LDPE). Suitable LDPE's have the following properties:Density: 910-930 kg/m³ (ISO 1183) MFR₂: 0.1 to 10 g/10 min (ISO 1133)Melting Temperature: 100 to 130° C. (ISO 11357/03)

However in a preferred embodiment, the sealing layer comprises apolyethylene copolymer or terpolymer with a C₃₋₁₀-alpha-olefin. Suitablecomonomers are propylene, 1-butene, 1-pentene, 1-hexene and 1-octene ofwhich butene, hexene and octene are preferred. Moreover, it is preferredif the copolymer is an LLDPE. Suitable LLDPE's can be produced usingZiegler-Natta or metallocene catalysis with MWD (Mw/Mn) between 2-20 andMFR₂ of 0.1 to 10 g/10 min. LLDPE polymers which have a bimodalmolecular weight distribution are ideally suited when packagingoperations involve deep drawing and low temperatures.

The amount of comonomer present in the polyethylene copolymer may varyfrom 0.1% to 15% by weight, preferably 5% to 10% by weight.

LLDPE's of use in the sealing layer are preferably manufacturedemploying normal Ziegler-Natta catalysts or single site catalysts as isknown in the art and have the following properties: Density: 910-930kg/m³ (ISO 1183) MFR₂: 0.1 to 10 g/10 min (ISO 1133) MeltingTemperature: 100 to 130° C. (ISO 11357/03)

Various commercially available polymers may be used as the LDPE or LLDPEin the sealing layer of the invention. Potential polymers includeBorstar FB2230, FB2310, FA5224, FG5190 (Borealis), ELITE 5400G (Dow) andDowlex 2045E (Dow).

In a more preferred embodiment, the sealing layer may be a mixture ofpolyethylene polymers, e.g. a mixture of two polymers or three polymers.For example, the sealing layer could be formed from a mixture of LDPE's,LLDPE's or from the combination of an LLDPE and an LDPE.

A particularly suitable sealing layer is formed from a mixture of LLDPEpolymers as described previously above, e.g. Borstar FB2230 and Elite5400G. It is preferred if one LLDPE is a single site catalyst producedLLDPE (mLLDPE) due to its high seal strength and hot tack properties. Asecond LLDPE may be a Ziegler Natta LLDPE which may help to minimise thecost of the film. Preferred mLLDPE's have 1-hexene or 1-octene as acomonomer whereas preferred Ziegler-Natta LLDPE's employ butene orhexene as a comonomer.

Where two LLDPE or LDPE polymers are employed in the sealing layer eachmay form up to 99 wt % of the sealing layer. Preferably however eachLLDPE should form up to 80 wt % of the sealing layer. Wherever possiblehowever, the skilled man will maximise the presence of the Ziegler-NattaLLPDE to minimise costs and this should preferably form the bulk of thesealing layer. The ratio of Ziegler LLDPE to MLLDPE may therefore befrom 2:1 to 5:1, e.g. the Ziegler-Natta LLDPE will form at least 75 wt %of the sealing layer.

An alternative and still yet further preferred embodiment involves a twoor three polymer sealing layer comprising one or two polyethylenepolymers and a polyethylene copolymer with a polar comonomer (fromhereon a polar copolymer) such as an acetate or an acrylate. Preferredare acrylate comonomers of which butyl acrylate and especially methylacrylate are especially favoured.

It is believed the polar copolymer aids adhesion between the variouslayers of the multilayer film. The polar copolymer should preferablycomprise between 1% to 40% by weight comonomer, e.g. 5 to 35%, morepreferably 10 to 25% by weight.

Where a mixture of polyethylene polymer and polar copolymer is employedas the sealing layer, the polar copolymer should form between 5 to 25%by weight of the sealing layer, preferably 10 to 20% by weight. TheLLDPE polymer or polymers should therefore form 75 to 95% by weight ofthe sealing layer in this embodiment, e.g. 80 to 90%. The sealing layermay consist essentially of LLDPE and the polar copolymer (i.e. onlyadditionally includes standard additives/preservatives etc).

The first layer should comprise a polypropylene polymer, preferably apolypropylene copolymer with a C₂₋₁₀-alpha-olefin comonomer such asethylene, butene or hexene, especially ethylene. By polypropylenepolymer is meant a polymer in which at least 70%, preferably at least80% by weight of the polymer comprises propylene monomer units. In oneembodiment the polypropylene polymer may be a homopolymer, i.e. wheresubstantially all, e.g. at least 99.5% wt of the monomer units arederived from propylene however copolymers of propylene are preferred dueto their superior toughness at low temperatures.

The amount of comonomer present may vary, however suitable ranges arefrom 1% to 30%, preferably 5 to 10% by weight.

Preferred polypropylene polymers for use in the first layer areheterophasic block copolymers or random copolymers. Heterophasic blockcopolymers will give the best low temperature toughness and hence bebest suited for frozen packs. Random copolymers give the film improvedtransparency. Suitable polymers have the properties below and can bemade using Ziegler-Natta or single site catalysis often in a two stagepolymerisation using conventional techniques: Density: 890-920 kg/m³(ISO 1183) MFR₂: 0.05 to 2 g/10 min (ISO 1133) Melting Temperature: 140to 180° C. (ISO 3146)

Commercially available copolymers include BHC5012 (Borealis), BA110CF,RB707CF and RB501BF (Borealis).

The first layer may also comprise a mixture of polymers as long as oneis a polypropylene polymer. Preferred additional polymers include LDPEor LLDPE polymers such as those described above in connection with thesealing layer. Preferred in this regard are mLLDPE's.

Where such a mixture is present, it is preferred if the polypropylenecopolymer forms 75 to 95% by weight of the first layer. The LLDPE orLDPE polymer may form between 5 to 25%, e.g. 8 to 18% by weight of thefirst layer.

Whilst the polymer film used for the packing of fresh produce in thisinvention should comprise a sealing layer and a first layer (i.e. atleast a bilayer film), the film may also comprise further layers. Forexample, a preferred film comprises three layers, a sealing layer, firstlayer and further sealing layer, e.g. arranged such that the sealinglayers sandwich the first layer. A second sealing layer may be differentfrom or identical to the first sealing layer and have a structure asdescribed above in connection with the main sealing layer. Convenientlyhowever, both sealing layers will be identical. A three layer film inwhich the first layer is sandwiched between two sealing layers isbelieved to curl less than a two layer film having only a first andsealing layer.

At least one sealing layer must always be outmost to allow sealing to beeffected.

The combination of the sealing layer and first layer of the inventiongives rise to a film which exhibits high temperature heat resistance andhence integrity during heat sealing as well as an advantageous sealingtemperature, i.e. sufficient to allow evaporation of water etc from thesealing areas of the film and an advantageous heat sealing range. Hence,due to the integrity of the film at higher temperatures, it is possibleto heat seal the film safely at higher temperature.

The films of the invention should preferably have a heat sealing rangeof at least 25° C., especially at least 30° C., most preferably at least40° C. (measured as described in the examples).

Moreover, the films of the invention are preferably heat sealable attemperatures greater than 180° C.

The films also exhibit high mechanical strength particularly at lowtemperature (e.g. −40° C.). Thus, the films of the invention exhibitvery high protrusion puncture probe test results (ASTM D5748) inparticular over a broad temperature range. Thus for a 130 μm film,maximum force is preferably greater than 170N, more preferably greaterthan 200N.

The films of the invention can be manufactured using conventionalcoextrusion and film blowing technology or via lamination. Hence thevarious layers can be coextruded through a suitable die as is known inthe art. Alternatively, the layers could be laminated, e.g. using apolyurethane adhesive however, this is not preferred since coextrusionis a simpler technique.

The polymers used in the multilayers films may be bought commerciallyfrom polymer suppliers or manufactured using conventional polymerisationtechniques. Thus, polymers manufactured using single site catalystsemploy procedures well known in the art. Published patent applicationsby Exxon, Hoechst, Phillips, Dow, Chisso, Mitsui, Fina, BASF,Mitsubishi, Mobil, BASF, Montell, DSM and Borealis, e.g. WO96/23010,WO98/49208, WO99/12981, WO99/19335, WO97/28170, EP-A-423101, EP-A-537130all have descriptions of the use of these catalysts.

Alternatively, the polymers may be made using Ziegler-Natta catalystse.g. in Borealis' Borstar® polymerisation technology or known highpressure radical polymerisation technologies.

The multilayer film should be approximately 50 to 500 microns inthickness, e.g. 80 to 250 microns. Typically, the polypropylene layer isapproximately twice as thick as the sealing layer(s).

The films of the invention are particularly applicable for packaginglines where the product is frozen immediately after packaging. Theinvention is thus of most importance for packaging meat and fish whichis frozen for both industrial and consumer consumption.

The actual packaging process may be a form, fill and seal (FFS) process,deep draw process or tray lidding process. FFS and deep draw processesare preferred, especially deep draw.

FFS involves packaging machines that use heat sealable flexible plasticpackaging film to form a package, which is then filled, heat-sealed andcut off. There are two basic types, horizontal and vertical. Ahorizontal machine forms a package, fills with product and seals, andall in a sequence of operations while the film is being transported in ahorizontal direction. They are widely used for packaging solidfoodstuffs. A vertical machine forms a tube, fills and seals, all in asequence of operations while the film is being transported verticallydownwards. They are widely used for packaging foodstuffs in a liquid,powder, paste or granule state.

Thus viewed from one aspect the invention provides a process forpackaging fresh produce comprising forming an open package using a filmcomprising a polypropylene polymer and a polyethylene polymer ashereinbefore defined, filling said package with said fresh produce, andheat-sealing the package.

In a deep draw process the film of the invention is deep drawn into asuitable container in which the fresh produce is placed. Sealing of thecontainer may be effected by using further film of the invention andsealing as necessary. It is most surprising that the films of theinvention are suitable for use in a deep draw process.

Thus, viewed from a further aspect, the invention provides a process forpackaging fresh produce comprising:

(I) Deep drawing a polyolefin film comprising a polypropylene polymerand a polyethylene polymer as hereinbefore described to form acontainer;

(II) placing said fresh produce in said container; and

(III) heat sealing the container with a second polyolefin filmcomprising a polypropylene polymer and a polyethylene polymer ashereinbefore defined.

In a tray lidding process, a preformed tray, made from conventionalmaterial, may be sealed using the film of the invention.

Surprisingly, in the FFS process, it is envisaged that a sealing layerformed entirely from MLLDPE can be employed.

Certain films of use in the packaging of fresh produce according to theinvention are themselves new and form a further aspect of the invention.Hence, viewed from a further aspect the invention provides a multilayerfilm having a first layer and a sealing layer, said first layercomprising a heterophasic polypropylene copolymer with a C₂₋₁₀-alphaolefin comonomer and said sealing layer comprising an LLDPE and anethylene acrylate copolymer, e.g. EMA polymer.

Viewed from a still further aspect the invention provides a process forthe manufacture of a multilayer film as hereinbefore describedcomprising coextruding a first layer and a sealing layer, said firstlayer comprising a heterophasic polypropylene copolymer with aC₂₋₁₀-alpha olef in comonomer and said sealing layer comprising an LLDPEand an ethylene acrylate copolymer and blowing the extrudate into afilm.

The raw materials used to make the films may also contain standardadditives such as antioxidants, anti-blocking agents, antic staticagents, slip agents, pigments, dyes etc. A number of the commerciallyavailable polymer grades of use in this invention already comprise oneor more of these additives.

The invention will now be described with reference to the followingnon-limiting examples.

EXPERIMENTAL

The films were prepared using the following equipment:

Extruder: Windmöller & Hölscher, coextrusion blown film line with IBC(internal bubble cooling).

3-layer, A/B/C, barrier screw

Typical thickness distribution: 25%/50%/25%

Die gap 1,2 mm

Die Ø 200 mm

Blow up ratio film 3:1

Temperature settings on the extruders 180° C.-240° C.

General Packaging Protocol

Films 1 to 4 described in the examples below were tested on acommercially available packaging machine, Repak RE 3 model from year2000/2001. A first film with 220 μm thickness was heated and deep drawnto form a tray, filled with fresh herring and a second film with 120 μmthickness was sealed on top making a lid.

Comparative Example 1

A coextruded film with three layers was prepared using the materialsbelow:

Sealing layer: 100% PE-LLDPE—Borstar FB2230

First layer: 100% PE-LLDPE—Borstar FB2230

Outside layer: 100% PE-LLDPE—Borstar FB2230

At normal sealing temperature settings for PE (145 to 155° C.) the sealdelaminated due to the presence of contaminants. When increasing thesealing temperature to 160° C., holes appeared beside the seals leadingto package failures.

Comparative Example 2

A coextruded film with three layers was prepared using the materialsbelow:

Sealing layer: 100% PE-LLDPE—Borstar FB2230

First layer: 100% PE-HDPE—Borstar FB1460

Outside layer: 100% PE-LLDPE—Borstar FB2230

At normal sealing temperature settings for PE (145 to 155° C.) the sealdelaminated due to the presence of contaminants. When increasing thesealing temperature to 160° C. holes appeared beside the seals leadingto package failures. This despite the fact that HDPE with higher meltingpoint was used in the first layer providing better heat resistance.

Example 3

A coextruded film with three layers was prepared using the materialsbelow:

-   -   Sealing layer: PE-LLDPE—Borstar FB2230 (70%)+PE LLDPE-mLLDPE—Dow        Elite 5400 (15%)+PE Copolymer with methyl acrylate—DuPont        Elvaloy 1224AC (15%)    -   First Layer: PP heterophasic Copolymer—Borealis BHC 5012        (85%)+PE LLDPE-mLLDPE—Dow Elite 5400 (15%)    -   Second sealing: PE-LLDPE—Borstar FB2230 (70%)+Layer PE        LLDPE-mLLDPE—Dow Elite 5400 (15%)+PE Copolymer with methyl        acrylate—DuPont Elvaloy 1224AC (15%)

At normal sealing temperature settings for PE (145 to 155° C.) the sealdelaminated due to the presence of contaminants. When-the sealingtemperature was increased to 160 to 165° C. a perfect/strong seal couldbe achieved with no delamination or holes appearing beside the seals.

Example 4

A coextruded film with two layers was prepared using the materialsbelow:

-   -   Sealing layer: PE-LLDPE—Borstar FB2230 (70%)+PE LLDPE-mLLDPE—Dow        Elite 5400 (15%)+PE Copolymer with methyl acrylate—DuPont        Elvaloy 1224AC (15%)    -   First Layer: PP heterophasic Copolymer—Borealis BHC 5012        (85%)+PE LLDPE-mLLDPE—Dow Elite 5400 (15%)

At normal sealing temperature settings for PE (145 to 155° C.) the sealdelaminated due to the presence of contaminants. When the sealingtemperature was increased to 160 to 165° C., a perfect/strong seal couldbe achieved with no delamination or holes appearing beside the seals.

Example 5

The mechanical performance of films has been analysed at +230° C. and−40° C. by the Protrusion Puncture Probe Test according to ASTM D5748 inorder to demonstrate the superior mechanical performance of films ofthis invention over a broad temperature range and their suitability forpackaging of goods to be frozen. The films of example 1 and 3 werecompared with the following film and that of Example 6. All films had atotal film thickness of 130 μm. The results are presented in Table 1.

Film of Example 5

Sealing layer: 100% PE-LLDPE—Borstar FB2310

First layer: 100% PE-LLDPE—Borstar FB2310

Outside layer: 100% PE-LLDPE—Borstar FB2310

Example 6

Nordform 213 from Nordpak OY, Finland, a commercially availablemultilayer laminate consisting of several layers of polyethylene andpolyamide with adjacent layers of adhesive polymer commonly used forfood packaging. TABLE 1 results ASTM D5748 Film No. Ex 1 Ex 3 Ex 5 Ex 6Temperature (° C.) 23 23 23 23 Max force (N) 120 220 132 164 Elongationat max force (mm) 71 103 74 52 Absorbed energy at max force (Nmm) 534613803 6211 4784 Temperature (° C.) −40 −40 −40 −40 Max force (N) 184 202158 179 Elongation at max force (mm) 37 39 41 29 Absorbed energy at maxforce (Nmm) 3915 4751 3834 2678

Example 7

The sealing behaviour of films has been analysed with a Toyoseiko typeHG-100 according to the following procedure:

-   (I) Two films are sealed to each other at a sealing temperature T (°    C.), sealing pressure of 2 bar and sealing time of 4 seconds.-   (II) The sealing temperature T (° C.) is varied in steps of 5° C.    between 120-180° C., the latter representing the maximum temperature    of the used apparatus.-   (III) The seal integrity is tested by pulling one end from each of    the two films apart with a tensile tester.-   (IV) At lower temperatures the seal will de-laminate or open due to    lack of proper sealing-   (V) The seal initiation temperature (T¹) is the lowest temperature    when the seal is not de-laminating but the film is elongating and    breaking at a random place.-   (VI) The maximum sealing temperature is exceeded when one of the    films snaps off at the edge of the seal. The recorded maximum seal    temperature (T²) is defined as 5° C. lower than this snap-off    temperature.-   (VII) The sealing range is defined as SR=T²−T¹

The films of Examples 1, 2 and 3 all with a total film thickness of 120μm, were compared and results presented in Table 2. TABLE 2 Film No. Ex1 Ex 2 Ex 3 Seal initiation temperature (° C.) T¹ 145 145 140 Maxsealing temperature (° C.) T² 150 175 >180 Sealing range T²-T¹ 5 30 >40

Example 8

The film of Example 3 was used for packaging of lettuce on a commercialpackaging machine from SFK of Denmark in order to demonstrate thesuitability of the film of the invention.

A first film with 220 μm thickness was heated and deep drawn to form a20 cm deep tray, filled with 1 piece of lettuce and a second film with70 μm thickness was sealed (155° C.) on top making a lid. The sealintegrity was afterwards tested by cutting a 25 mm strip of film andloaded with 100N in a conventional tensile testing equipment.

Result

The film could be deep drawn without thin spots or holes, the seal hadno leakage and did not delaminate during tensile testing.

Example 9

The film below was used for packaging of pre-boiled potatoes in water ona commercial packaging machine, Tiromat Powerpack 620, 2001 model, inorder to demonstrate the suitability of the film of the invention in thepackaging operation and for reheating of the potatoes—still in thepackage—in boiling water as well as in a microwave oven.

-   -   Sealing layer: PE-LLDPE—Borstar FB2230 (85%)+PE-LLDPE-mLLDPE—Dow        Elite 5400 (15%)    -   First layer: PP Heterophasic Copolymer—Borealis BHC5012        (85%)+PE-LLDPE-mLLDPE—Dow Elite 5400 (15%)    -   Second sealing Layer: PE-LLDPE—Borstar FB2230        (85%)+PE-LLDPE-mLLDPE—Dow Elite 5400 (15%)

A first film with 170 μm thickness was heated and deep drawn to form a 5cm deep tray, filled with 9 pre-boiled potatoes and a second film with100 μm thickness was sealed (130° C.) on top making a lid while beingunder vacuum. The packs were heated and tested in the following ways:

A—In water

The pack with potatoes was put into boiling water and kept there for 10minutes.

The packs showed no deformation or change in its shape.

The packs maintained the vacuum.

The packs could not be torn open by hand.

The potatoes were entirely warm and had a fully acceptable taste andtexture.

This procedure was repeated for 10 packages with same result.

B—In microwave oven

The pack with potatoes was heated in a conventional microwave oven at350 watt for 10 minutes.

The packs showed no deformation or change in its shape. The packsmaintained the vacuum.

The packs could not be torn open by hand.

The potatoes were entirely warm and had a fully acceptable taste andtexture.

This procedure was repeated for 10 packages with same result.

The film could be deep drawn without thin spots or holes, the seal hadno leakage and did not delaminate during tensile testing. Heating in didnot damage the packaging.

1-19. (canceled)
 20. A method for the packaging of meat or seafood inwhich the meat or seafood is packaged on a packaging line using amultilayer film having at least a first layer and a sealing layer, saidfirst layer comprising a heterophasic polypropylene block copolymer andsaid sealing layer comprising a polyethylene polymer wherein the packageis frozen immediately after packaging.
 21. A method as claimed in claim20 for the packaging of fish.
 22. A method as claimed in claim 20wherein said heterophasic polypropylene polymer is a copolymer ofpropylene with a C₂₋₁₀-alpha olefin.
 23. A method as claimed in claim 20wherein said sealing layer comprises an LDPE or LLDPE.
 24. A method asclaimed in claim 23 wherein said sealing layer comprises an LDPE orLLDPE and a polyethylene copolymer with a polar comonomer.
 25. A methodas claimed in claim 24 wherein said polar comonomer is an acrylatecomonomer.
 26. A method as claimed in claim 20 wherein said sealinglayer comprises an LLDPE.
 27. A method as claimed in claim 26 whereinsaid sealing layer comprises an mLLDPE and an LLPDE made byZiegler-Natta catalysis.
 28. A method as claimed in claim 20 whereinsaid propylene copolymer is a heterophasic ethylene propylene copolymer.29. A method as claimed in claim 20 wherein said first layer comprisesan LLPDE.
 30. A method as claimed in claim 20 wherein said multilayerfilm has 3 layers.
 31. A method as claimed in claim 11 wherein saidthree layer film contains two identical sealing layers sandwiching afirst layer.
 32. A method as claimed in claim 20 further comprisingcoextruding said first layer and a sealing layer, said first layercomprising a heterophasic polypropylene copolymer with a with aC₂₋₁₀-alpha olefin comonomer and said sealing layer comprising an LLDPEand an ethylene acrylate copolymer, and blowing the extrudate to formsaid multilayer film.
 32. A method as claimed in claim 20 comprising:(I) Deep drawing said multilayer film to form a container; (II) placingsaid meat or seafood in said container; (III) heat sealing the containerwith a second multilayer film as defined in any one of claims 1 to 11;and (IV) immediately freezing the container.
 33. A method as claimed inclaim 20 comprising forming an open package using said multilayer film,filling said package with said meat or seafood, heat-sealing the packageand immediately freezing the package.
 34. A multilayer film having afirst layer and a sealing layer, said first layer comprising aheterophasic polypropylene block copolymer with a C₂₋₁₀-alpha olefincomonomer and said sealing layer comprising an LLDPE and an ethyleneacrylate copolymer.